The present inventive concept relates to a light emitting device. More particularly, the inventive concept relates to a light emitting device having a light emitting structure, such as an LED, and a substrate to which the light emitting structure is attached and through which light produced by light emitting structure is transmitted.
Light emitting devices such as those employing light emitting diodes (LEDs) emit light when electrons and holes are combined. The light emitting devices have several advantages including low power consumption, extended life span, being installable without spatial limitation, and robustness against vibration.
One of the most challenging issues with respect to developing light emitting devices is to improve their light extraction efficiency. Light extraction efficiency is defined as a ratio of light escaping into the ambient (i.e., air or transparent resin covering a light emitting device) to light generated within the light emitting device. A gallium nitride (GaN) substrate has an optical refractive index of about 2.5 which is greater than that of air or a transparent resin. When light generated within the GaN substrate is incident upon an interface between two media at an angle greater than a critical angle, the incident light undergoes total internal reflection (TIR) and is trapped in the GaN substrate and cannot escape into the air or transparent resin. This may detract from the light extraction efficiency of the device.